Well drilling fluid and process



"atent ii flfice 3,fl25,234 Patented Mar. 13, 1962 3,025,234 WELLDRILLHNG FLUED AND lROCESS Peter J. Canterino, Bartlesville, Okla,assignor to Phillips Petroleum Company, a corporation of Delaware NDrawing. Filed Sept. 3, 1957, er. No. 683,427 39 Claims. (Cl. 2528.5)

This invention relates to drilling fluids. In one aspect it relates todrilling fluids, such as the aqueous and emulsion types, used indrilling oil and gas wells, or other deep wells. In another aspect, itrelates to a method of drilling such wells with a novel drilling fluidcharacterized by a desirably low filtration rate or water loss, andother desirable rheological properties. In a further aspect it relatesto a method of controlling the filtration rate of a drilling fluid bytreating the same with a novel additive.

In the art of drilling wells to tap subterranean deposits, such as gasor oil, especially when drilling by the rotary method or the percussionmethod wherein cuttings must be removed from the bore hole, it isnecessary to use a drilling fluid, as is Well known to those skilled inthe art. The especially prepared drilling fluid is pumped down a hollowdrill string or stem within the bore hole, across the drill bit which isattached to the lower end of the drill stem, and is then normallycirculated upwardly through the annular space between the drill stem andthe bore hole. Circulation of the drilling fluid in this manner removesthe cuttings from the bore hole, lubricates and cools the drill bit,seals the wall of the bore hole with a thin, impervious layer of solidmaterial or filter cake, and applies a hydrostatic head to the formationto counterbalance formation pressures.

In addition to having desirable rheological properties such as viscosityand gel strength, it is very important that the drilling fluid exhibit alow rate of filtration or water loss, that is, the drilling fluid mustprevent excessive amounts of fluid from flowing from the bore hole intothe surrounding formation. The loss of water or other fluid from thedrilling fluid is prevented by the formation of the filter cake whichdeposits from the drilling fluid and seals the wall of the bore hole.Where porous zones or fissures or cracks are encountered, the seal orfilter cake must prevent rapid loss of fluid into the surroundingformation by filtration due to the pressure gradient. If the filtrationrate is excessive, a thick filter cake can be formed whether or not thedrilling fluid is circulating and whether or not drilling is inprogress. Swelling and dispersion of shales can also be controlled byeffectively sealing the wall of the bore hole with a drilling fluidhaving a low filtration rate.

Seepage of fluid from the formation into the bore hole is also preventedby the filter cake. If water, for example, filters or seeps into theformation penetrated, several problems arise; the producing formationmay be contaminated by the water, permanently displacing the oil andblock production; or, if the formation penetrated is of the heavingshale type, the latter may absorb water from the drilling fluid and by acaving or swelling action common to bentonitic materials, close the borehole around the drill stem, choke off circulation of drilling fluid, andseize the drilling stem so that it twists in half.

Accordingly, an object of this invention is to provide a novel drillingfluid. Another object is to provide an improved method of drilling oiland gas wells, and other deep Wells, using a drilling fluid which hasbeen treated or conditioned so as to lessen the tendency of thisdrilling fluid to lose or gain water to or from the formationpenetrated. A further object is to provide a novel drilling fluid, suchas the aqueous or emulsion type, containing a small but effective amountof a water-soluble or dispersible polymer prepared by polymerizingvinyl-substituted heterocyclic nitrogen compounds with carboxycontainingcomonomers having a terminal vinyl group and their hydrolyzableprecursors. A still further object is to provide a method forcontrolling the water loss of a drilling fluid. Further objects andadvantages of this invention will become apparent from the followingdiscussion and appended claims.

Broadly, I have discovered the water loss or filtration rate of adrilling fluid can be substantially minimized or reduced by treating thedrilling fluid with water-soluble or water-dispersible polymers ofpolymerizable vinylsubstituted heterocyclic nitrogen base compounds andcopolymerizable carboxy-containing compounds having a terminal vinylgroup, and their hydrolyzable carboxyyielding precursors. These polymerscan be in the form of acids or salts thereof.

The polymerizable heterocyclic compounds include five and six memberedheterocyclic compounds containing a hetero nitrogen atom. Thesepolymerizable heterocyclic nitrogen compounds are those containing avinyl group, viz.,

l CH2=C- where R is a hydrogen atom or a methyl group. One or two vinylgroups can be attached to the hetero ring, and also alkyl groups can beattached to the hetero ring as long as there are not more than 12 carbonatoms in the total of these alkyl groups. One oxygen atom can also beattached by a double bond to one of the carbon atoms in the hetero ring.Furthermore, one or two benzoid structures can be attached or fused tothe hetero ring, including nuclear (ring) alkyl-substituted derivativesthereof (again, not more than 12 carbon atoms in the total of thesealkyl groups), the ring of each benzoid structure being completed withany pair of vicinal carbon atoms in the hetero ring. This class ispolymerizable heterocyclic nitrogen compounds can be represented broadlyby the formulas:

where I and II are selected from the group consisting of saturated andunsaturated hetero rings, n is a positive integer from 1 to 2, R isselected from the group consisting of H and CH R is selected from thegroup consisting of H, alkyl groups (not more than 12 carbon atoms beingpresent in the total of said alkyl groups), an oxygen atom attached by adouble bond to one of the carbon atoms in the hetero ring, and thosenonmetallic atoms necessary to complete from 1 to 2 benzoid structureseach of which is completed in part with any pair of vicinal carbon atomsin the hetero ring, said benzoid structures including nuclear (ring)alkyl-substituted benzoid rings (again, not more than 12 carbon atoms inthe total of the alkyl substituents).

A more narrower class of polymerizable heterocyclic a nitrogen compoundsfor preparing the polymers of this invention can be represented by theformulas:

R (C=CH2) n wherein n is a positive integer from 1 to 2, R is selectedfrom the group consisting of H and CH and R is selected from the groupconsisting of H and alkyl groups, not more than 12 carbon atoms beingpresent in the total of said alkyl groups.

Typical heterocyclic nitrogen compounds which are applicable in thepractice of this invention representatively include those of thepyrrolidine series (e.g., N-vinylpyrrolidine,2-methyl-5-vinylpyrrolidone, etc.), those of the pyrroline series (e.g.,N-vinylpyrroline, 2-vinylpyrroline, etc.), those of the pyrrole series(e.g., N-vinylpyrrole, 3-vinylpyrrole, 4-vinylpyrrole, 3-methyl-4-vinylpyrrole, 2,4-dimethyl-3-vinylpyrrole, etc.), those of thepyrrolidone series (e.g., N-vinyl-2-pyrrolidone, N vinyl 5 methyl 2pyrrolidone, 3 vinylpyrrolidone, 3-ethyl-4-vinyl-2-pyrrolidone, etc.),those ofpyrrolone series (e.g., N-vinyl-2-pyrrolone,3-vinyl-2-pyrrolone, etc.), those of the indole series (e.g.,N-vinylindole, 3-methyl-2-vinylindole, N-vinyl-2,3-dimethylindole,7'-methy1-3-vinylindole, etc.), those of the indolenine series (e.g.,3-vinylindolenine, 2-vinyl-3,6-dimethylindolenine, etc.), those of theindoline series (e.g., N vinylindoline, 2,7 dimethyl 2 vinylindoline,etc.), those of the carbazole series (e.-g., N-vinylcarbazole, N vinyl3,7 dimethylcarbazole, N vinyl 2 methyl- 3,6-diethylcarbazole, etc.),those of the piperidine series (e.g., N-vinylpiperidine,2-vinylpiperidine, '3-vinylpiperidine, 2,3 dimethyl 5 vinylpiperidine,3,4 dimethyl- S-butyl-G-Vinylpiperidine, N-vinyl-3-propylpiperidine, 3,N-divinyl-S-ethylpiperidine, etc.), those of the pyridone series (e.g.,N vinyl 3 pyridone, 5 vinyl 2 pyridone, N-vinyl-2-methyl-4-pyridone,etc.), those of the piperidone series (e.g., N vinyl-4-piperidone,2-vinyl-6- methyl-4-piperidone, N-vinyl-2-piperidone, etc.), those ofthe pyridine series (e.g., N-vinyl-1-2-dihydropyridine,N-vinyltetrahydropyridine, 2-vinylpyridine, 4-vinylpyridine,2-vinyl-5-ethylpyridine, S-methyl-Z-vinylpyridine,5-ethyl-2-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-5-vinylpyridine, 4-methyl-3-vinylpyridine, 2-isopropenylpyridine,5-propyl-Z-isopropenylpyridine, 3-dodecyl-4,5- divinylpyridine,2-decyl-S-isopropenylpyridine, 2-octyl- S-vinylpyridine,2,4,6-trimethyl-S-vinylpyridine, 3,4,5,6- tetramethyl 2 vinylpyridine,3,5 diisopropenylpyridine, 2,6-diethyl-4-vinylpyridine,2,4-dimethyl-5,6-dipentyl 3 vinylpyridine, 2 isopropyl 4 nonyl 5vinylpyridine, Z-methyl-S-undecyl-G-vinylpyridine, 2,5-divinylpyridine,3-methyl-2,S-divinylpyridine, etc.), those of the quinoline series(e.g., 2-vinylquinoline, Z-methyl-S-vinylquinoline,2,8-dimethyl-3-vinylquinoline, 2,3,8-trimethyl- "5-vinylquinoline,2-vinyltetrahydroquinoline, 8-ethyl-2- vinylquinoline,4-hexyl-5-vinylquinoline, 2,5-divinylquinoline, etc.), those of theisoquinoline series (e.g., l-vinylisoquinoline,S-methyl-l-isopropenylisoquinoline, 1,8-divinylisoquinoline,3,5-divinylisoquinoline, 6,7-dimethyl 3,5-divinylisoquinoline, etc.) andthe like.

The carboxy-containing comonomers, and their hy- 4t drolyzableprecursors, copolymerizable with one or more of the above-mentionedpolymerizable vinyl-substituted heterocyclic nitrogen compounds, can berepresented by the formula:

where R is selected from the group consisting of H, lower alkyl (e.g.,CH C H C3H7, etc.), Cl, COOH, CN, CONH COOR and CH COOR (R' being alower alkyl), and A is selected from the group consisting of COOH, CN,CONH COOR (R" being a lower alkyl), and COOM, said M being a monovalentsalt-forming radical selected from the group consisting of alkali metal,such as sodium or potassium, and ammonium radicals.

Typical carboxylic acids and their hydrolyzable acidforming precursorsrepresentatively include unsaturated aliphatic carboxylic acids, such asacrylic acid, methacrylic acid, ethacrylic acid, propacrylic acid,2-chloroacrylic acid, Z-cyanoacrylic acid, 2-carboxyacrylic acid, etc.;nitriles, such as acrylonitrile, methacrylonitrile, ethacrylonitrile,etc.; the corresponding amides, such as acrylamide, methacrylamide,ethacrylamide, 2-carboxylacrylamide, 2- cyanoacrylamide,Z-methylenemalonamide, etc.; esters, such as methyl acrylate, ethylacrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, methylethacrylate, ethyl ethacrylate, 2-chloromethyl acrylate, methyl 2-carboxylacrylate, ethyl Z-carbamylacrylate, ethyl 2-cyanoacrylate,diethyl 2-methylenemalonate, etc.; and watersoluble alkali metal andammonium salts, such as sodium acrylate, sodium methacrylate, potassiumacrylate, potassium ethacrylate, ammonium acrylate, ammoniummethacrylate, sodium 2-carboXyacrylate, sodium Z-carbamylacrylate,sodium ethyl-Z-methylenemalonate, etc. These acids and their precursorsgenerically are compounds which under hydrolyzable conditions contain acarboxy groupwhich conditions are well known to chemists and need not bedescribed in detail herein.

The polymers of this invention can be water-soluble or dispersiblepolymers prepared by any conventional polymerization procedure, such asemulsion polymerization, solution polymerization, suspensionpolymerization, or the like. In the preferred method of preparing thesepolymers, the monomers are prepared by emulsion polymerization wherebythe monomers are first emulsified in water containing an emulsifyingagent, such as a soap, and polymerization is promoted by a suitablecatalyst, such as a redox catalyst system consisting of salts of apersulfate and a sulfite. Satisfactory rates of polymerization inemulsion form can be obtained at temperatures below C. At the end of thereaction, which can be completed in about 1 hour, the polymer can berecovered from the reaction medium by filtration or the like and treatedwith an alkali, such as sodium hydroxide, or ammonium hydroxide, so asto hydrolyze or saponify the ester groups of the carboxy-formingcomonomer or to hydrolyze the nitrile or amide groups of thecarboxyforming comonomer. Preferably, this hydrolysis is effected in theemulsion prior to recovering the polymer. The resulting polymers containcarboxy groups and may be purified. The free acid as well as the saltsthereof formed by neutralization, metathesis, ion exchange, etc., areuseful in controlling the water loss of drilling fluids. These saltsinclude the water-soluble metal and ammmonium or organic base salts,especially the alkali or alkaline earth metal salts. Other metal saltsinclude aluminum, iron, copper, lead, zinc and other heavy metals, andthe like.

It is not essential to hydrolyze the polymer prior to its addition tothe drilling fluid. In many cases, this can be efiected under theconditions prevailing in the drilling fluid or the latter can beadditionally treated to promote or accelerate the hydrolysis. The freeacid as well as other water-insoluble salts can be renderedwater-soluble or dispersible in situ the drilling fluid.

In polymer chemistry it is common to refer to a copolymer in terms ofthe weight ratio per 100 parts of total weight of the monomers used toprepare the copolymer. Thus, when 75 parts of monomer A and 25 parts ofmonomer B are copolymerized, the resulting copolymer can be referred toas a 75/25 copolymer of A and B or a copolymer prepared with 75 parts ofA per 100 parts total weight of the monomers. It is understood that thepolymer may not contain exactly the same ratio of the two monomer unitsas was used in the preparation of the polymer. However, it is thepractice in the polymer art to base the range for polymer composition onthe charge ratio of the monomers rather than on their combined ratio. Itis recognized that the combining ratio of monomers varies during thecourse of the polymerization so that if the polymerization is conductedto 100 percent conversion, the average combining ratio will then beequal to the charge ratio of the monomers. To fully utilize themonomers, it is desirable in the practice of this invention to conductthe polymerization to at least 50 percent conversion of the polymers. Aminor amount of the vinyl-substituted heterocyclic nitrogen base monomeris preferably used per 100 parts of the total monomer weight. Generally,definite advantages can be gained by using as little as about 3 parts toat least as much as 50 parts of the heterocyclic nitrogen monomer per100 parts of total monomer weight. Preferably, about 5 to about 30 partsby weight of the heterocyclic nitrogen base monomer is used per 100parts of total monomer weight. More than two monomers can be used in thepolymerization recipe, that is, terpolymers can be formed as well ascopolymers; however, about 3 to 50 parts by weight of the total of theheterocyclic compounds should be used per 100 parts of total monomers.

Although the preferred hcterocyclic nitrogen compounds to be used inpreparing the polymers of this invention have only one vinyl groupattached to the hetero ring, heterocyclic nitrogen compounds having twovinyl groups attached to the hetero ring can be used, preferably alongwith monovinyl heterocyclic nitrogen compounds when up to 2 percent,preferably less than 0.5 percent, of the divinyl compound is used.

The polymers used in this invention are unique in that the moleculescontain both acidic and basic groups so that the polymers can bedescribed as amphoteric. As such, they can be made water-soluble ordispersible (the term dispersible being generic).

Any of the drilling fluids of the aqueous or emulsion types now in usemay be treated with the polymers of this invention to control thefiltration rate thereof. Drilling fluids which can be so treated includeaqueous drilling fluids, usually comprising water, colloidal material ofboth gel-forming and non gel-forming types and weighting materialssuspended in the water. Either salt water or fresh water can be used inmaking up the drilling fluids and inorganic solid materials, such asbentonitic and other clays, can be suspended in the drilling fluid. Limetreated drilling fluids, low pH and high pH drilling fluids, etc., canalso be treated with the polymers of this invention.

Moreover, drilling fluids of the emulsion type, such as oil-in-wateremulsions and water-in-oil emulsions can also be treated. These emulsiondrilling fluids can be prepared from water and a hydrocarbon fluid suchas crude oil, diesel fuel, kerosene, gas oil, heavy fuel oil, variouspetroleum fractions, blends of such fractions with asphalt or otherviscous oil, and the like. These emulsion drilling fluids can beprepared using oil soluble emulsifying agents, such as alkaline earthmetal salts of saponifiable oils such as vegetable oils, wood oils andfish oils. Blown or oxidized asphalt and the alkali metal and alkalineearth metal salts of lignin can be used. These emulsion drilling fluidscan be prepared by methods well known to those skilled in the art. Theamount of hydrocarbon fluid employed in preparing these emulsiondrilling fluids will depend upon various considerations such as the typeof emulsion desired, the amount of water, the density of the drillingfluid, the nature of the formation penetrated, the amount of emulsifier,and other factors that can be readily determined by those skilled in theart. Generally, for oil-in-water emulsions, the amount of oil componentemployed will be in the range between about 2 and 40 percent (commonlybetween about 5 and percent) by volume of the final emulsion. For thewater-in-oil systems, the amount of the oil component employed will bein the range between about 20 and 95 percent (commonly between about 40ad 60 percent) by volume of the final emulsion.

The drilling fluids of this invention can contain, in addition to thepolymers added according to this invention to control the filtrationrate of the drillingfluid, the

usual drilling fluid constituents, as for example clay and drilledsolids, caustic, quebracho, lime, barite, tannins, polyphosphate, mica,cotton seed hulls, cellophane scrap. and the like. The water-soluble ordispersible polymers of this invention can be added by any convenientmanner to the drilling fluid. The polymer can be predissolved ordispersed in water or in water containing other desirable drilling fluidreagents such as sodium hydroxide, sodium carbonate, lignitic shale,quebracho, disodium acid pyrophosphate, etc. A particularly convenientmethod is to add the polymer additive through a jet mixer or at thesuction of the drilling fluid pumps, thereby achieving rapid dispersionand effectiveness. Solutions or suspensions containing the polymer, orthe polymer in essentially dry conditions, can be used. The drillingfluids treated in accordance with this invention are circulated duringdrilling and a new method of drilling is obtained since the drillingfluid has a low filtration rate, desirable viscosity, and otherdesirable drilling fluid properties which expedite the drillingoperation, and thereby increase the recovery of oil or gas.

The amount of polymer to be added to the drilling fluid will depend uponvarious factors, such as the type of formation penetrated, the type ofdrilling fluid, the depth of the formation, prior treatment of thedrilling fluid and borehole, etc. Accordingly, I prefer to define thelimits of amounts of the polymer additive to be employed in the drillingfluids of my invention by functional rather than by actual numericallimits, the amount to be used being that necessary to give the resultdesired, i.e., a drilling fluid having a relatively low rate offiltration or Water loss. An overor under-dose of the polymer will stillbe operative but merely does not produce optimum results. In general,polymer added to the drilling fluid in the range from about 0.1 to about10 pounds of polymer per barrel (42 US. gallons) of drilling fluid willbe adequate. Beneficial eflects can, however, be achieved usingconcentrations of polymer higher than 10 pounds per barrel, for example25 pounds per barrel, particularly when it is desired to minimizedispersion of shales or when the drilling fluid contains lowconcentrations (i.e., less than 5-10 percent by weight) of claymaterials.

The following specific examples set forth hereinafter are illustrativeof this invention and specific details for operating the presentinvention are described with comparative results showing the advantagesto be obtained by this invention. However, these examples do not undulylimit this invention and merely illustrate preferred embodimentsthereof.

EXAMPLE I Polymers were prepared by emulsion polymerization of methylacrylate with 0, 5.0, 10, 20, 25, 30, 40, or 50 parts of2-methyl-5-vinylpyridine per parts of total monomers. The recipes usedin the preparation of these polymers are given in Table I.

Table I RECIPES USED FOR PREPARATION OF THE POLYMERS Ingredient Parts byweight 500 500 600 500 500 500 500 500 500 100 97. 5 95 90 80 75 70 6050 2methyl-5-vinvy1pyridine. 2. 5. 0 20 25 30 40 50 Sulfonated castoroil 1. o 1. 0 1. 0 1. 0 1. 1. 0 1. 0 1. 0 1. 0 Potassium pcrsulfate. 1.0 1. 0 1. 0 1. O 1. 1. 0 1. 0 1. 0 1. 0 Sodium acid sultite- 1.0 1. 0 1.0 1. 0 1. 1. 0 1. 0 1. 0 1. 0 Acetic acid (glacial) 0. 0 2. 0 5. 1 11.222. 28.0 3 .6 45 56 The ingredients for the preparation of each polymerwere added to a flask, stirred and heated to a temperature of about 60C. Heating was terminated and the heat of reaction increased thetemperature to a maximum value of about 85 C. At the end of one hour,the polymerization was essentially complete and a solution containingsodium hydroxide was added to effect saponification of the ester and toneutralize the acetic acid. The amount of alkali used was equivalent tothe amount of ester and acetic acid. The mixture was heated for 3 hoursat 80 C. to effect saponification. The total solids in the resultingviscous solution was determined by drying an aliquot of the solution at105 C. From the value for the total solids and the computed ratio of thepolymer to salts in the solids, the percent by weight of the polymer insolution was computed.

The solutions containing the polymers were used to prepare salt waterdrilling fluids. Each drilling fluid sample was prepared in thefollowing manner: suflicient polymer solution was taken to give 3.0 g.of polymer, and the solution was diluted with water. The amount of waterused was computed to give a 350 ml. total volume of the prepareddrilling fluid after addition of attapulgite clay (14.1 g.) and ofsodium chloride (17.1 g), respectively. The mixture was vigorouslystirred for 30 minutes. The drilling fluid was then placed in a Masonjar and aged for 16 hours at 80 C. At the end of the aging period thedrilling fluid was cooled to room temperature, stirred for about minutesand tested according to the procedure described in Recommended Practiceon Field Procedure for Testing Drilling Fluids, A.P.I. Code No. 29.

The water-loss and the pH values of the drilling fluids are reported inTable II. The apparent viscosities were determined with a Fann V-GMeter.

The results reported in Table II illustrate the benefits to be gained byusing the copolymers of this invention. These results show that optimumresults for Water loss control were obtained when the polymer wasprepared from the mixture containing 10 parts by weight of theheterocyclic nitrogen monomer; however, desirable properties wereobtained with those polymers prepared with from about 3 to 50 parts byweight of the heterocyclic nitrogen monomer.

EXAMPLE II For purposes of comparison, a saponified 90/ 10 methylacrylate/styrene polymer was prepared and a salt water drilling fluidtreated therewith. This polymer was prepared from the following recipe.

Table III Ingredient: Parts by weight Water 450 Methyl acrylate 10Styrene 1.0 Potassium persulfate 1.0 Sulfonated caster oil 1.0 Sodiumacid sulfite 0.5 Dodecyl mercaptan 0.01

The first five ingredients were heated at 50 C. with stirring for 1%hours, after which the acid sulfite and mercaptan were added. The heatof reaction raised the temperature of the mixture to C. and after anhour at this temperature, 40 g. of sodium hydroxide was added to efiectsaponification in situ. Heating was continued at Table IV Water ApparentPolymer added pH loss, ml. viscosity,

/10 aorylate/styrene 8. 7 50. 3 5 D 9. 3 50. 1 4 Do.- 10. 7 60.2 4 90/10acrylate/Z-methyl-5-vinylpyridinc 8. 7 10 4 The superiority of thevinyl-substituted heterocyclic copolymer of this invention as a waterloss controlling additive over that of an acrylate/styrene copolymer isquite evident from Table IV.

EXAMPLE III In this example, comparative tests were made on drillingfluids containing in one case a commercial polymer sold for use indrilling fluids, i.e., Cypan, a polyacrylate, and a polymer of thisinvention, i.e., a saponified /5 acrylonitrile/Z-methyl-S-vinylpyridinepolymer.

The saponified 95/ 5 acrylonitrile/Z-methyl-5-vinylpyridine polymer wasprepared by emulsion polymerization using the following recipe.

Table V Ingredient: Parts by weight Water 450 Fatty acid soap 2.5Acrylonitrile 47.5 Z-methyl-5-vinylpyridine 2.5 Potassium persulfate 0.5Dodecyl mercaptan 0.05

The reactants were charged to a quart-size bottle which was agitated ina constant temperature bath at 40 C.

9 After 18 hours the reaction mixture was diluted with approximately anequal volume of isopropyl alcohol and 10 Table VII stirred for 15 to 20minutes. The coagulated polymer partsbyweightmr was recovered byfiltration. The moist cake of copolymer was air-dried at about 55 C. Aportion (41 g.) of the gredient Acrylic acid: product was placed in aliter flask containing 27 g. of Poly-acrylate N g y pyrsodium hydroxidedissolved in about 500 cc. of water. mhdone The mixture was heated 3-4hours at 85 C. to eflect Wate 500 500 saponification. Duringsaponification the off-white polyf g"" 100 0 mer changed to a deep redcolor and eventually dissolved %Cry11e1acid 1 d 8 53 to give a lightamber solution. Inherent viscosity of the g f ifgfigfi gg fi g L0 0,0 dt i water was 11 7 Potassiumpersulfate" 1.0 1.0 Thirty g. of theaforementioned polymer solution, con- Sodmm amd Sumte m raining 3 g. ofthe saponified 95/5 acrylonitrile/2-methyl- 7 5-vinylpyridine polymer,was added to 307 ml. of water 15 ig: 33 52223 aifiiitf 8mm field arechemical equwalent to 90 which had been mixed with 14.1 g. ofattapulgite clay and 17.4 g. of sodium chloride. The salt water drillingEach polymer was P p by Placmg e gs fluid was aged for 16 hours at 80 C.The water loss in a flask, Stirred thell heating to to Inmate P yvalue fthe drilling fl id was determined by filt i g merization. Heating wasthen terminated, but the reacthe drilling fluid at 85 C., maintainingthe filter press 20 tioll Continued as evidenced by the increase in e atthis temperature by means of a surrounding bath. lure of the mi Xture toabout After eompletlon The filtration rate observed after 30 minutes,while apply- 0f the Polymenzatien 0f the Polyaerylate, Sedlllm Y ing apressure of 100 p.s.i.g., was doubled in order to coride Was added in an'f equivalent to the ester and rect for the area of the filter press andthereby make the the ester Saponified y heallng the mixture to Qbeutdimensions comparable to that stated in A.P.I. Code No. for 3 hours- Theacrylic aeid/N-vinylpyrfolldone (11d 29 for tests conducted at ambienttemperatures. Results not require Saponifieation to form free eafbexylgroups are given i Table V since acrylic acid was used as the comonomer.The reac- A drilling fluid containing the commercial polyacrylate, tionj l eentalning the Polymers Were Used 10 P Cypan, was prepared in amanner analogous to that de- P drllllllg fiuldsscribed for thepreparation of drilling fluid containing the 30 The effects of each of iP y on two yp of 95 5 copolymer except that the polyacrylate was a drydrilling fluids were determined, v1z., a fresh water drillsalt andtherefore 335 ml. of water was used in preparing a fluld and a SaltWater dfilllng flllld- The fresh Water the drilling fluid. A controlsample of drilling fluid was drfuing fluid eontained Mecl'aeken y, anative y prepared i a i il manner i h no polymer added), m1ned nearMcCracken, Kansas; the concentration of containing 4.1 g. of attapulgiteclay and 17.4 g. of sodie clay was about 20 Percent by Welght of thedrilling um chloride in 337 ml. of water. Filtration rates of the fiuld-A Polymer solution containing about 1 to 3 drilling fluid containing thepolyacrylate and the control the Polymer basls) was added to the claySuspenslon were obtained in a similar manner at a temperature f andsuflicient water was then added together with sodium 85 C. and theresults obtained are also set forth in Table hydroxide so that thefotalYolume was 350 1 f purposes f comparison 40 The salt water drilllngfluids were prepared in a similar manner using comparable amounts ofpolymer solution, VI 14.1 g. of attapulgite clay and 17.4 g. of sodiumchloride P1YmeI added= Water 1055 (ml) per 350 ml. of drilling fluid.Both types of drilling fluids None (control) 184 were stirred todisperse the clay. These drilling fluids polyacrylaie ".'"-T were sealedin Mason jars and aged at 80 C. for 16 hours.Acrylomtnle/z'methyl's'vmylpyndme After aging, the drilling fluids werecooled, stirred 30 The marked advantage of using a polymer of vilminutes and tested in accordance with the procedure of substitutedheterocyclic nitrogen/carboxyl comonomer Code along With SuitableControl Samples over a commercial polymer of polyacrylate in controlling0f drilling fluid- The results Obtained are given in Table the waterloss of a drilling fluid is evident from Table VI. For thesedeterminations, eomperison was made EXAMPLE IV a with the polyacrylatesalt and acryllc acid/N-vinylpyrro-lidone polymer of this inventionusing drilling fluids A sodium polyacrylate, similar to that often usedin having closely comparable pH values. These pH values drilling fluidsof the prior art, and a copolymer, acrylic were determined with anelectronic pH meter using a acid/N-vinylpyrrolidone, described by thisinvention, were calomel and glass electrode system carefully calibratedprepared by emulsion polymerization using the following with standardbuffer solutions and compensated for recipes. temperatures.

Table VIII Fresh water drilling fluid Salt water drilling fluid Polymeradded Polymer, NaOH, Water Apparent Polymer. NaOH, Water Apparentlbjbbl. lb./bbl. pH loss, viscosity, lb./bbl. 1b./bbl. pH loss,viscosity,

ml. cp. m1. cp.

None (control) 0 0 6.38 54. 5 0 O 184 1 0 6.78 39 11 a 0 9.01 3 3 1.59.1 3.7 13 a o 3.7 11 1 0 6.8 30.2 14 3 0.3 9.0 21.6 3 Dol. 3 1 9.2 2.622 Acrylic acid/N-vinlypyrrolidoue 1 1.5 6. 7 2. 5 16 3 1.6 9. 10 13. 54

Do 3 2.0 9.01 2.4 46 Do 3 1.5 7.12 2.8 41

1 Prepared by saponification of poly (methyl acrylate). 2 Prepared byneutralization of polyacrylic acid.

These results show the improvement in water loss control which can beachieved by using a polymer prepared from a vinyl-substitutedheterocyclic nitrogen base compound, e.g., N-vinylpyrrolidone, and acarboxy containing comonomer having a terminal vinyl group, e.g.,acrylic acid. This improvement leads to a substantial economy inconcentration polymer and is particularly pronounced in salt waterdrilling fluids.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art Without departing from the scopeand spirit of this invention. The foregoing discussion and examplesmerely illustrate preferred embodiments of this invention and do notunduly limit the same.

I claim:

1. In a process of drilling a well with well drilling tools, the stepsof circulating in said Well a drilling fluid to which has been added aminor but sufiicient amount to substantially reduce the filtration rateof said drilling fluid of a polymer prepared by polymerizing avinyl-substituted heterocyclic nitrogen compound and a comonomer havinga terminal vinyl group and under hydrolyzing conditions contains acarboxy group.

2. The process according to claim 1 wherein the amount of saidheterocyclic nitrogen compound used in preparing said polymer is in therange from about 3 to about 50 parts per 100 parts of total monomerweight.

3. The process according to claim 1 wherein said heterocyclic nitrogencompound has the formula:

where I is a ring selected from the group consisting of saturated andunsaturated hetero rings, n is a positive integer from 1 to 2, R isselected from the group consisting of H and CH and R is selected fromthe group consisting of H, alkyl groups having not more than 12 carbonatoms in the total of said R groups, an oxygen atom attached by a doublebond to one of the carbon atoms in said hetero rings, and thosenon-metallic atoms necessary to complete from 1 to 2 benzoid structureseach of which is completed in part with any pair of vicinal carbon atomsin said hetero rings.

4. The process according to claim 1 wherein acid heterocyclic nitrogencompound has the formula:

where I is a ring selected from the group consisting of saturated andunsaturated hetero rings, 11 is a positive integer from 1 to 2, R isselected from the group consisting of H and CH and R is selected fromthe group consisting of H, alkyl groups having not more than 12 carbonatoms in the total of said R groups, an oxygen atom attached by a doublebond to one of the carbon atoms in said hetero rings, and thosenon-metallic atoms necessary to complete from 1 to 2 benzoid structureseach of which is completed in part with any pair of vicinal carbon atomsin said hetero rings. a

5. In a process of drilling a well with Well drilling tools, the stepsof circulating in said Well a drilling fluid which forms a filter cakeon the wall of said well, the steps of treating said drilling fluid byadding to the same a minor but sufficient amount to reduce thefiltration rate of said drilling fluid of a polymer prepared bypolymerizing a vinyl-substituted heterocyclic nitrogen compound and acomonomer having the formula:

where R is selected from the group consisting of H, lower alkyl, Cl,COOH, CN, CONH COOR and CH COOR,

12 said R being a lower alkyl, and A is selected from the groupconsisting of COOH, CN, (TONI-I COOR, and COOM, said R being a loweralkyl, and said M being a monovalent salt forming radical selected fromthe group consisting of alkali metal and ammonium radicals.

6. The process according to claim 5 wherein said heterocyclic nitrogencom-pound has the formula:

where R is selected from the group consisting of H and CH and R isselected from the group consisting of H and alkyl groups having not morethan 12 carbon atoms in the total of said R 7. The process according toclaim 5 wherein said heterocyclic nitrogen compound has the formula:

where R is selected from the group consisting of H and CH and R isselected'from the group consisting of H and alkyl groups having not morethan 12 carbon atoms in the total of said R 8. The process according toclaim 5 wherein said heterocyclic nitrogen compound has the formula:

Er k

where n is a positive integer from 1 to 2, R is selected from the groupconsisting of; I 1; and CH and R is selected from the group consistingof H and alkyl groups having not more than 12 carbon atoms in the totalof said R 9. The process according to claim 5 wherein said heterocyclicnitrogen compound has the formula:

Where n is a positive integer from 1 to 2, R is selected from the groupconsisting of H and CH and R is selected from the group consisting of Hand CH and R is selected from the group consisting of H and alkyl groupshaving not more than 12. carbon atoms in the total of said R 11. Theprocess according to claim 5 wherein the amount of said heterocyclicnitrogen compound used in preparing said polymer is in the range fromabout 3 to about 50 parts per parts of total monomer weight.

12. The process according to claim 11 wherein said drilling fluid is ofthe aqueous type.

13. The process according to claim 11 wherein said drilling fluid is ofthe fresh water type containing suspended clayey materials.

14. The process according to claim 11 wherein said drilling fluid is ofthe oil-in-water emulsion type.

15. in a process of drilling a well with well drilling tools, the stepsof circulating in said well a salt water drilling fluid containingsuspended clayey materials which form a filter cake on the wall of saidwell, the steps of treating said drilling fluid by adding to the same aminor but sufficient amount to reduce the filtration rate of saiddrilling fluid of a polymer prepared by polymerizing a vinyl-substitutedheterocyclic nitrogen compound and a comonomer having the formula:

where R is selected from the group consisting of H, lower alkyl, 01,COOH, CN, CONH COOR and CH COOR, said R being a lower alkyl, and A isselected from the group consisting of COOH, ON, CONE-I COOR", and COOM,said R being a lower alkyl, and said M being a monovalent salt formingradical selected from the group consisting of alkali metal and ammoniumradicals, wherein the amount of said heterocyclic nitrogen compound usedin preparing said polymer is in the range from about 3 to about 50 partsper 100 parts of total monomer weight.

16. The process according to claim 15 wherein said polymer is the sodiumsalt of a saponified 95/5 copolymer of acrylonitrile andZ-methyl-S-vinylpyridine.

17. In a process of drilling a well with well drilling tools, the stepsof circulating in said well an emulsion drilling fluid containing oiland salt water, the steps of treating said drilling fluid by adding tothe same a minor but sufficient amount to reduce the filtration rate ofsaid drilling fluid of a polymer prepared by polymerizing avinyl-substituted heterocyolic nitrogen compound and a comonomer havingthe formula:

where R is selected from the group consisting of H, lower alkyl, 01,COOH, CN, COHN COOR' and CH COOR', said R being a lower alkyl, and A isselected from the group consisting of COOH, CN, CONH COOR", and COOM,said R" being a lower alkyl, and said M being a monovalent salt formingradical selected from the group consisting of alkali metal and ammoniumradicals, wherein the amount of said heterocyclic nitrogen compound usedin preparing said polymer is in the range from about 3 to about 50 partsper 100 parts of total monomer weight.

18. The process according to claim 17 wherein said polymer is the sodiumsalt of a saponified 95/5 copolymer of acrylonitrile and2-methyl-5-vinylpyridine.

19. In a process of drilling a well with well drilling tools, the stepsof circulating in said Well a drilling fluid comprising salt water andto which has been added a minor but suflicient amount to substantiallyreduce the filtration rate of said drilling fluid of a polymer preparedby polymerizing a vinyl-substituted heterocyclic nitrogen compound and acomonomer having a terminal vinyl group and under hydrolyzing conditionscontains a carboxy group.

20. A well drilling fluid containing a minor but suflicient amount tosubstantially reduce the filtration rate of said drilling fluid of apolymer prepared by polymerizing a vinyl-substituted heterocyclicnitrogen compound and a comonomer having a terminal vinyl group andselected from the group consisting of carboXy-containing compounds andtheir hydrolyzable carboxy-yielding precursors.

21. A well drilling fluid according to claim 20 wherein saidheterocyolic nitrogen base compound has the formula:

where I is a ring selected from the group consisting of saturated andunsaturated hetero rings, n is a positive integer from 1 to 2, R isselected from the group consisting of H and CH and R is selected fromthe group consisting of H, alkyl groups having not more than 12 carbonatoms in the total of said R groups, an oxygen atom attached by a doublebond to one of the carbon atoms in said hetero rings, and thosenon-metallic atoms necessary to complete from 1 to 2 benzoid structureseach of which is completed in part with any pair of vicinal carbon atomsin said hetero rings.

22. A well drilling fluid according to claim 20 wherein saidheterocyclic nitrogen base compound ha the formula:

l Br I (C=CH2) u where I is a ring selected from the group consisting ofsaturated and unsaturated hetero rings, 21 is a positive integer from 1to 2, R is selected from the group consisting of H and CH and R isselected from the group consisting of H, alkyl groups having not morethan 12 carbon atoms in the total of said R groups, an oxygen atomattached by a double bond to one of the carbon atoms in said heterorings, and those non-metallic atoms necessary to complete from 1 to 2benzoid structures each of which is completed in part with any pair ofvicinal carbon atoms in said hetero rings.

23. The well drilling fluid according to claim 20 wherein the amount ofsaid heterocyclic nitrogen compound used in preparing said polymer is inthe range from about 3 to about 50 parts per parts of total monomerweight.

24. The well drilling fluid according to claim 20 where in said drillingfluid is of the aqueous type.

25. The well drilling fluid according to claim 20 wherein said drillingfluid is of the fresh water type containing suspended clayey materials.

26. The well drilling fluid according to claim 20 wherein said drillingfluid is of the oil-in-water emulsion type.

27. The well drilling fluid according to claim 20 wherein said polymeris acrylate/ N-viny1pyrrolidone.

28. The well drilling fluid according to claim 20 wherein said comonomeris represented by the formula:

R CH2=(|3A where R is selected from the group consisting of H, loweralkyl, Cl, COOH, CN, CONH COOR, and CH COOR, said R being a lower alkyl,and A is selected from the group consisting of COOH, CN, CONH COOR, and'COOM, said R being a lower alkyl, and said M being a mono-valent saltforming radical selected from the group consisting of alkali metal andammonium radicals.

29. The well drilling fluid according to claim 28 wherein saidheterocyclic nitrogen compound has the formula:

where R is selected from the group consisting of H and CH and R isselected from the group consisting of H and alkyl groups having not morethan 12 carbon atoms in the total of said R 15 30. The well drillingfluid according to claim 28 wherein said heterocyclic nitrogen compoundhas the formula:

where R is selected from the group consisting of H and CH and R isselected from the group consisting of H and alkyl groups having not morethan 12 carbon atoms in the total of said R 31. The Well drilling fluidaccording to claim 28 wherein said heterocyclic nitrogen compound hasthe formula:

i Br t about).

where n is a positive integer from 1 to 2, R is selected from the groupconsisting of H and CH and R is selected from the group consisting of Hand alkyl groups having not more than 12 carbon atoms in the total of R33. The Well drilling fluid according to claim 28 Wherein saidheterocyclic nitrogen compound has the formula:

where n is a positive integer from 1 to 2, R is selected 16 from thegroup consisting of H and CH and R is selected from the group consistingof H and alkyl groups having not more than 12 carbon atoms in the totalof R 34. A Well drilling fluid containing anacrylate/N-vinylpyr-rolidone polymer in an amount from about 0.1 to 10pounds per barrel, said polymer being prepared with from about 3 toparts of N-vinyl-pyrrolidone per 100 parts of total monomeric weight.

35. A well drilling fluid containing an acrylate/2-methyl-S-vinylpyridine polymer in an amount from about 0.1 to 10 poundsper barrel, said polymer being prepared with from about 3 to 50 parts ofZ-methyl-S-vinylpyridine per 100 parts of total monomeric Weight.

36. A salt Water well drilling fluid containing susended clayey materialand a minor but suflicient amount to substantially reduce the filtrationrate of said drilling fluid of a polymer prepared by polymerizing avinyl-substituted heterocycli'c nitrogen compound and a comonomer havinga terminal vinyl group and selected from the group consisting ofcarboxy-containing compounds and their hydrolyzable carboxy-yieldingprecursors.

37. The drilling fluid according to claim 36 wherein said polymer is thesodium salt of a saponifled /5 copolymer of aorylonitrile and2-methyl-5-vinylpyridine.

38. An emulsion well drilling fluid containing oil and salt water and aminor but suiflcientamount to substantially reduce the filtration rateof said drilling fluid of a polymer prepared by polymerizing avinyl-substituted heterocyclic nitrogen compound and a comonomer havinga terminal vinyl group and selected from the group consisting ofcarboxy-containing compounds and their hydrolyzable carboxy-yieldingprecursors.

39. A well drilling fluid containing salt Water and a minor butsuflicient amount to substantially reduce the filtration rate of saiddrilling fluid of a polymer prepared by polymerizing a vinyl-substitutedheterocyclic nitro gen compound and a comonomer having a terminal vinylgroup and selected from thegroup consisting of carboxycontainingcompounds and their hydrolyzable carboxyyielding precursors.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,025,234March 13, 1962 Peter J. Canterino It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 12, lines 8 to 14, the formula should appear as shown belowinstead of as in the patent:

I c=cn column 13, line 43, for "COHN read CONH Signed and sealed this14th day of August 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. IN A PROCESS OF DRILLING A WELL WITH WELL DRILLING TOOLS, THE STEPSOF CIRCULATING IN SAID WELL A DRILLING FLUID TO WHICH HAS BEEN ADDED AMINOR BUT SUFFICIENT AMOUNT TO OF A POLYMER PREPARED BY POLYMERIZING AVINYL-SUBSTITUTED HETEROCYCLIC NITROGEN COMPOUND AND A COMONOMER HAVINGA TERMINAL VINYL GROUP AND UNDER HYDROLYZING CONDITIONS CONTAINS ACARBOXY GROUP.